Traditional optical fingerprint sensor devices, such as shown in FIG. 1, use a prism or a component equivalent to the prism, such as grating, to capture fingerprint images, but suffer from perspective distortion in which an image is skewed and distorted. Holographic phase grating to the prism was added to normalize the optical axis of an imaging lens 110 to the plane of the imaging lens. Problems with such devices include: (1) external light would creep in and essentially create noise within the image contrast leading to a loss of definition of the image, (2) dirt and residue which remained on the prism or reflecting face would blur and obstruct the scanned image, (3) image distortion, as previously mentioned above, and (4) the difficulty in receiving images of different sizes due to the preset length between the corrective lens and the imaging device. Another form of prior art sensor calls for a series of prisms, comprising of light emitters and detectors, to compensate for the distortion problem. This prior art approach, however, occupies too much space and limits flexibility.
Accordingly, there is a need to provide a fingerprint sensor using anamorphic optics, which mitigates the distortion problem, is flexible in size, and has the ability to obtain different or optimum images.